This invention relates to cooling of thin wall structures and, more specifically, of thin wall ceramic structures. The cooling structure of the present invention has one or more channels that lie between two opposing surfaces of a thin wall structure.
Various means of cooling thin wall structures are known in the art. The necessity for such cooling exists for airfoils such as the blades or stator vanes of a gas turbine engine, for combustion structural elements of gas turbine engines, for rocket and jet engine exhaust nozzles, for the skin structure of high performance aircraft, and for other high temperature environment applications. In particular, turbine stators of advanced engines operate at a turbine inlet temperature far exceeding the capability of cooled superalloy material, even when coated with a thermal barrier coating, while at the same time advanced engines need to reduce cooling flow. Cooled ceramics have the potential to yield viable stator and blade designs for these demanding operating conditions.
An example of a structure for cooling a ceramic airfoil blade for a gas turbine engine is disclosed in U.S. Pat. No. 4,314,794, issued Feb. 9, 1982. In this application, segmented hollow ceramic washers are assembled with provision for airflow into the hollow portion. The cooling airflow then passes through the ceramic wall structure by transpiration facilitated by a porous ceramic wall. The emphasis is on cooling by cool airflow from an interior cavity to the external surface of the blade. Disadvantages to this design include the requirement for construction of the airfoil from a plurality of washers stacked cooperatively, as well as the requirement for use of a structural material that facilitates transpiration cooling. Both of these structural elements introduce unnecessary complexity and cost to the airfoil.
Another example of a ceramic structure use of through wall cooling flow is found in U.S. Pat. No. 5,030,060, issued Jul. 9, 1991. In this instance, cooling air conduit passages are formed to pass air from an interior chamber metal wall to an exterior ceramic surface wall or layer. The intent is for a cool air film to exist over the ceramic outer layer to prevent hot gas direct impingement on the surface of the ceramic layer. Both this structure and others, which use through wall cooling, are limited in cooling efficiency for reduction of blade surface temperature.
As can be seen, there is a need for a more efficient means of cooling thin wall structures such as found in gas turbine engines. The present invention incorporates the use of in-wall conduits to channel cooling fluid flow between the two opposing surfaces of, for example, ceramic wall gas turbine engine blades.
An improved thin wall cooling structure of the present invention comprises one or more channels formed between the two opposing surfaces of a thin wall structure. The channels traverse the thin wall structure generally parallel to the wall surfaces with cooling fluid exit and entry openings at the edge of the wall structure. Depending on the cooling requirements and cooling fluid characteristics, as well as the composition of the thin wall structure, the cooling channels vary in cross section dimension and the path between entry and exit openings. Also, the direction of coolant flow within one channel relative to another may be varied such as same direction flow (i.e., coflow) or opposed (i.e., counterflow).
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.